Method for cooling heated adsorbent beds

ABSTRACT

Method and apparatus for cooling a heated regenerated bed in a gas sorption process. Cooling gas is continually circulated through the heated bed in a closed cooling circuit; by maintaining a positive back pressure on the cooling circuit, no gas is permitted to leave the cooling circuit during the cooling step.

United States Patent Inventor Clem A. Barrere, Jr.

Ponca City, Okla.

Appl. No. 753,487

Filed Aug. 19, 1968 Patented May 11, 1971 Assignee Continental OilCompany Ponca City, Okla.

METHOD FOR COOLING HEATED ADSORBENT BEDS 15 Claims, 2 Drawing Figs.

US. Cl 55/62, 55/ l 80 Int. Cl B01d 53/04 Field ofSearch 55/59, 62,

[56] References Cited UNITED STATES PATENTS 2,880,818 4/1959 Dow 55/623,008,539 11/1961 Francis, Jr. 55/62 3,109,722 11/1963 Dow 55/213,121,002 2/1964 Kilgore et al.. 55/180X 3,238,701 3/1966 Holt 55/203,479,797 1 l/ 1969 Spencer et a]. 55/62 Primary Examiner-lohn AdeeAttorneysJoseph C. Kotarski, Henry H. Huth, Jerry B.

Peterson, Van D. Harrison, Jr., Carroll Palmer and Kemon, Palmer andEstabrook ABSTRACT: Method and apparatus for cooling a heatedregenerated bed in a gas sorption process. Cooling gas is continuallycirculated through the heated bed in a closed cooling circuit; bymaintaining a positive back pressure on the cooling circuit, no gas ispermitted to leave the cooling circuit during the cooling step.

IN EFFLUENT GAS FROM COOLING CIRCUIT MOL PER CENT OF PROPANE AND HEAVIERHYDROCARBONS TIME IN MINUTES Patented May 11, 1971 3577;867

2 Sheets-Sheet 1 MOL PER CENT OF PROPANE AND HEAVIER HYDROCARBONS INEFFLUENT GAS FROM COOLING CIRCUIT O 5 IO I5 20 TIME IN MINUTES AF/G.

INVENTOR. CLEM A. BARRERE JR.

AGE/VT METHOD FOIR COOLING HEATED ADSORBENT IBEDS This invention relatesto the recovery of condensables from gas streams through the use ofsorbent beds. More specifically, it is concerned with the cooling ofheated sorbent beds which have been heated to remove adsorbedcondensables andwhich must now be cooled prior to their being contactedwith a feed gas stream containing vaporized condensables.

The recovery of gasoline, light hydrocarbons, water, or other vaporizedcondensables from natural gas or other gas sources by flowing the gasstream through a sorbent bed, or adsorber, is well known. As usedherein, the term vaporized condensables includes a readily availablecondensable gas, such as gasoline, other liquid hydrocarbons and water.Each sorbent bed, when saturated with adsorbed condensables, isregenerated by heating, usually by circulating a heated gas through thebed. The heated gas is then cooled at some point in the heating circuitand the condensed liquids are collected and removed as one of thedesired products. In several schemes of recovery a series of beds arecycled through a sorbent phase in a sorption circuit, a heating orregenerating phase in a heating or regenerating circuit, and finallythrough a cooling phase in a cooling circuit. The cooling phase isdesigned to bring the heated, regenerated body to a temperature where itcan again be exposed to the flowing stream of raw feed gas in thesorption circuit.

In one method of cooling the heated bed, a portion of the residue gasfrom the bed in the sorption circuit is flowed through the heated bed.In many process schemes this gas, after it flows through the bed beingcooled, is discarded from the system. In several schemes the cooling ofthe heated bed is preceded by a displacement, or purge step, whereinheated regeneration gas present in the newly heated bed is displacedfrom it prior to the cooling step. This displacement, or purge step, isdesigned to prevent loss of the rich regeneration gas in the heated bedwhen subsequently it is placed in an open circuit cooling system.

I have now detemtined that in the cooling process, although the bedbeing cooled may have previously been submitted to a displacement orpurge step, as much as 20 percent of the adsorbed condensables presentin the bed prior to its being placed in the heating circuit are retainedwithin the sorbent bed after it has been heated and purged. Thisfraction of adsorbed condensables is subsequently released to thecooling gas stream flowed through the bed during the cooling step.Obviously, if this stream of cooling gas is vented from the system, aserious loss of recoverable product occurs. For example, FIG. I showsthe condensable content of the effluent gas from a typical bed in acooling circuit for a minute cooling phase which originally wassaturated with condensables from a hydrocarbon gas stream, heated tovaporize the adsorbed condensables and purged. It is obvious that evenafter the purge steps, a substantial amount of condensables is releasedduring the first l2 minutes of the cooling period.

An object of this invention is to increase the recovery of condensablehydrocarbons from a hydrocarbon-bearing gas.

Another object of this invention is to improve the efficiency of gastreating systems utilizing sorbent beds to recover condensablehydrocarbons.

Another object of this invention is to reduce the loss of adsorbedcondensables from a heated sorbent bed when subsequently it is cooled byflowing a cooling gas therethrough.

Other objects of the invention will become apparent from the followingdescription and disclosure of my invention.

With respect to the accompanying FIGS:

FIG. 1 has been discussed above and depicts the change in concentrationof condensables in the effluent gas stream from a heated, regeneratedbed being cooled in a typical open or closed cooling cycle as thecooling step proceeds.

FIG. 2 depicts a conventional three-bed gas treating system in whichthere is a sorption circuit, cooling circuit, and heating circuit.

As previously stated, my invention comprises retaining all of thegascirculating through a bed in the cooling circuit within the circuitor, stated another way, preventing the escape of any of the circulatinggas from the cooling circuit.

More specifically, in a process for the recovery of condensables from agas stream wherein a sorbent body is contacted with the gas stream andthe sorbent body containing sorbent condensables is heated to vaporizesaid condensables, my invention is the method of cooling the heatedsorbent body in a cooling circuit comprising:

a. flowing a stream of cool gas into the heated sorbent body;

b. removing an effluent stream of gas from the heated sorbent body; 1

c. cooling the effluent stream of (b);

d. returning the cooled effluent stream to the stream of cool gas of(a); and

e. retaining substantially all of the circulating stream of gas withinthe flow path defined by steps (a), (b), (c), and (d).

As discussed previously, a substantial amount of the recoverable,condensed hydrocarbons originally present in a sorbent bed prior to itsbeing heated is lost during the subsequent cooling steps if the coolinggas is vented from the bed without further treatment. The fraction ofcondensables present in the effluent cooling gas from the bed beingcooled may be as high as 13 mol-percent at the beginning of the coolingcycle. The fraction of condensables will diminish as the cooling stepcontinues but may remain at an appreciably high level for an extendedperiod, so that a substantial loss of product occurs.

FIG. 2 represents a preferred embodiment of our invention and depictsgenerally a three-bed gas treating system in which there are sorption,cooling and heating circuits.

The sorption circuit comprises a raw feed gas source flowing throughconduit 4. The raw feed gas flows through adsorber l where condensablesare adsorbed and stripped; residue gas flows out through conduit 5. Suchsorption circuits are, of course, well known in the prior art.

The heating circuit comprises, in general, a heating gas con duit 6which conducts heated, regeneration gas to adsorber 3, conduit 7 whichconducts effluent gas from adsorber 3 to cooler 8, conduit 9, separator10, conduit 11, gas blower l2, conduit 13, and heater 14 to complete theclosed heating circuit. Heating circuits of this type are generallyknown, and are used to vaporize condensables adsorbed by a sorbent bedin a sorption circuit as discussed previously.

The cooling circuit depicted in FIG. 2 includes cooling gas conduit 15,which conducts cooling gas to the adsorber 2. Adsorber 2 is a heatedsorbent body from which most of the adsorbed condensables have beenremoved by a hot stream of gas in a heating circuit as described above.Effluent gas from adsorber 2 flows through conduit 16, gas blower l7,conduit 18, cooler 19, conduit 20 and is returned to adsorber 2. Asdepicted in FIG. 2, conduit 21 connects the cooling circuit and thesorbent circuit. A check valve 22 is located intermediate conduit 21 andpermits flow only from conduit 4 to conduit 20. As cooling gas iscirculated through adsorber 2, the temperature within the circuitdeclines; correspondingly, the pres sure also declines, due to theshrinkage of gas volume. The gas pressure in conduit 21 is maintained ata pressure in excess of that in the cooling circuit. Consequently, aspressure in the cooling circuit decreases, a volume of gas will flowthrough conduit 21 into the cooling circuit, and accordingly, no gasever leaves the cooling circuit during the cooling step. As adsorber 2is cooled, the condensables present in the recirculated cooling gas areadsorbed in the cooler portion of the adsorber bed, normally the topmostpart of the adsorber. In the event pressure in conduit 20 ever exceedsthe pressure in conduit 4, check valve 22 prevents the escape of gasfrom conduit 20 into conduit 4.

As noted previously, adsorber 2 prior to its being cooled may besubjected to a gas purge or displacement step.

FIG. 2 shows the feed gas in conduit 4 being used as the gas source toimpose a back pressure on the cooling circuit by means of conduit 21. Itwill be apparent that some other back pressure source of relatively leangas can be utilized as well. For example, the residue gas line 5 couldbe used, as long as the pressure therein is in excess of the gaspressure in the cooling circuit.

EXAMPLE Raw feed gas is processed by a system as shown in FIG. 2.Adsorbers l, 2 and 3 each operate about 20 minutes in the sorptioncircuit, 20 minutes in the heating circuit and 20 minutes in'the coolingcircuit for a 60-minute cycle time. Each adsorber is switched from onecircuit to the next in response to the measurement of the exit gastemperature in conduit 7 reaching 250 F. Feed gas in conduit 4 is atabout 80 F. and 500 p.s.i.a. and flows at a rate of 22,600 Mcf/day.Adsorbers l, 2, and 3 each have a volume of 570 ft, and operate at apressure of about 450 p.s.i.a. to 550 p.s.i.a. Each adsorber containsabout 16,000 lbs. of activated carbon (8 to 10 mesh). Adsorbenttemperature is about 120 F. during adsorption, a maximum of 600 F. andan average of 500 F. during reactivation and is cooled to about 200 F.during the cooling phase. Residue gas in an amount of about 17,400Mcf/day at about 100 to 250 F. and 490 p.s.i.a. is produced by way ofconduit 5. Reactivation gas is circulated in conduit 6 in an amount ofabout 15,700 Mcf/day at about 625 F. and 490 psia. Gas in conduit 7 hasa temperature of about 140 F. Separator 10 operates at about 80 F. and485 p.s.i.a. Raw liquid product is removed by way of conduit 22 in anamount of about 50,000 gal/day. Cooling gas circulates through thecooling circuit in an amount of about 19,000 Mcf/day at 495 p.s.i.a. and90 F. Heater 14 is designed for a duty of l4 l0 Btu/hr. Averagecompositions at various points throughout the system are tabulatedbelow:

M01 percent CeHil CH4 CzHt CaHs C4H1o CsHro plus M01 percent CaHu CH4CgHs CaHs C Hm CsHm plus 'Ilme lapsed:

Recirculation of this gas to the adsorber in the cooling circuitprevents the loss of 320 gallons of liquid product per cycle. None ofthis product is lost through conduit 21 since the gas pressure inconduit 21 is maintained always in excess of that in conduit 20.

Having thus described the invention by providing a specific examplethereof, it is to be understood that no undue limitations orrestrictions are to be drawn by reason thereof and that many variationsand modifications are within the scope of the invention.

1 claim:

1. In a process for the recovery of condensables from a gas streamwherein a cool sorbent body is contacted with said gas stream and saidsorbent body containing sorbent condensables is heated to vaporize saidcondensables, the method of cooling said heated sorbent body forrecontacting said gas stream which comprises:

a. flowing a stream of cool gas into said heated sorbent bodies;

b. removing an effluent stream of gas from said heated sorbent body;

0. cooling said sorbent effluent stream of (b);

d.'returning said cooled effluent stream to said stream of cool gas of(a); and I e. retaining essentially all of said circulating stream ofgas within the flow path defined by steps (a), (b), (c), and (d) bymaintaining a gas back pressure on the flow path defined by said steps(a), (b), (c), and (d) said back pressure being sufficient to maintainsaid gas within said defined flow path.

2. The method of claim 1 wherein step (e) comprises maintaining a gasback pressure on the flow path defined by steps (a), (b), (c), and (d)from an exterior gas pressure source, said back pressure beingsufficient to maintain said gas within said defied flow path.

3. The method of claim 2 wherein the source of said back pressure is alean gas.

4. The method of claim 3 wherein said lean gas is a feed gas.

5. The method of claim 3 wherein said lean gas is stripped residue gas.

6. A cyclical process'for the recovery of condensables from a raw feedgas stream comprising:

a. flowing said raw gas stream through a sorbent body whereincondensables are adsorbed;

b. removing a stripped residue gas stream from said first sorbent body;

c. flowing a heated regeneration gas stream through said sorbent bodywherein condensables are adsorbed thereby heating said sorbent body andvaporizing condensables into said flowing heated gas streams;

d. cooling said flowing heated gas stream thereby condensing saidvaporized condensables;

e. collecting said condensed condensables of (d);

f. flowing a cooling gas stream through said heated sorbent body of (c);

g. cooling the eflluent stream of cooling gas from said heated sorbentbody of (f);

h. recycling all of the cooled effluent gas stream of (g) to the heatedsorbent body of (f);

i. maintaining said cooling gas stream in fluid communication with asource of gas at a pressure sufficient to maintain said cooling gasstream within its defined flow path; and

j. confining all gas entering the flow path defined by steps (f), (g),and (h) to said flow path.

7. The method of claim 6 wherein said source of gas in (i) is said feedgas stream of (a).

8. The method of claim 6 wherein said source of gas in (i) is saidstripped residue gas stream of (b).

9. The method of claim 6 wherein said source of gas in (i) is a gasother than the feed gas stream of (a) and the stripped residue gasstream of (b).

10. The method of claim 6 wherein each of a series of sorbent bodies issequentially cycled through the steps of claim 6.

11. The method of claim 6 wherein prior to said stepv of cooling of (d)the gas present in said heated sorbent body of (c) is displaced by alean gas into another sorbent body in which said step of flowing aheated regeneration gas of (c) 12. The method of claim 1 wherein step(e) comprises retaining essentially all of said circulating stream ofgas within the flow path defined by steps (a), (b), (c), and (d) bymeans of a check valve situated in a conduit between said flow path andan exterior gas pressure source.

13. The method of claim 12 wherein the exterior gas pressure source isthe lean gas pressure source.

14. The method of claim 12 wherein the exterior gas pressure source is afeed gas pressure source.

15. The method of claim 12 wherein the exterior gas pressure source is astripped residue gas pressure source.

UNITED STATES PATENT OFFICE PC1-1055 W69) CERTIFICATE OF CORRECTION3,577,867 Dated July 8, 1971 Clem A. Barrere, Jr.

Patent No.

Inventor-(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Co1umn line 15 should read "said defined flow path" Column 4, line 58should read "which said step of flowing a heated regeneration gas of (c)is next to be conducted.

Signed and sealed this 23rd day of November 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Acting Commissioner of PatentsAttesting Officer

2. The method of claim 1 wherein step (e) comprises maintaining a gasback pressure on the flow path defined by steps (a), (b), (c), and (d)from an exterior gas pressure source, said back pressure beingsufficient to maintain said gas within said defied flow path.
 3. Themethod of claim 2 wherein the source of said back pressure is a leangas.
 4. The method of claim 3 wherein said lean gas is a feed gas. 5.The method of claim 3 wherein said lean gas is stripped residue gas. 6.A cyclical process for the recovery of condensables from a raw feed gasstream comprising: a. flowing said raw gas stream through a sorbent bodywherein condensables are adsorbed; b. removing a stripped residue gasstream from said first sorbent body; c. flowing a heated regenerationgas stream through said sorbent body wherein condensables are adsorbedthereby heating said sorbent body and vaporizing condensables into saidflowing heated gas streams; d. cooling said flowing heated gas streamthereby condensing said vaporized condensables; e. collecting saidcondensed condensables of (d); f. flowing a cooling gas stream throughsaid heated sorbent body of (c); g. cooling the effluent stream ofcooling gas from said heated sorbent body of (f); h. recycling all ofthe cooled effluent gas stream of (g) to the heated sorbent body of (f);i. maintaining said cooling gas stream in fluid communication with asource of gas at a pressure sufficient to maintain said cooling gasstream within its defined flow path; and j. confining all gas enteringthe flow path defined by steps (f), (g), and (h) to said flow path. 7.The method of claim 6 wherein said source of gas in (i) is said feed gasstream of (a).
 8. The method of claim 6 wherein said source of gas in(i) is said stripped residue gas stream of (b).
 9. The method of claim 6wherein said source of gas in (i) is a gas other than the feed gasstream of (a) and the stripped residue gas stream of (b).
 10. The methodof claim 6 wherein each of a series of sorbent bodies is sequentiallycycled through the steps of claim
 6. 11. The method of claim 6 whereinprior to said step of cooling of (d) the gas present in said heatedsorbent body of (c) is displaced by a lean gas into another sorbent bodyin which said step of flowing a heated regeneration gas of (c)
 12. Themethod of claim 1 wherein step (e) comprises retaining essentially allof said circulating stream of gas within the flow path defined by steps(a), (b), (c), and (d) by means of a check valve situated in a conduitbetween said flow path and an exterior gas pressure source.
 13. Themethod of claim 12 wherein the exterior gas pressure source is the leangas pressure source.
 14. The method of claim 12 wherein the exterior gasprEssure source is a feed gas pressure source.
 15. The method of claim12 wherein the exterior gas pressure source is a stripped residue gaspressure source.